The present invention relates to a parallel mechanism structure for controlling three-dimensional position and orientation.
As well known, generally, a parallel mechanism structure for controlling three-dimensional position and orientation has been chiefly studied for a work machine for processing a work object and a robot manipulator for assembling and transferring an object.
By way of example, the work machine functions to process a material, so that the material takes a desired shape or form. The work machine is composed of a machine body and a tool, in which the machine body operates by virtue of power-and a cutting tool works the material. At this time, it is essentially required that three-dimensional position and orientation of the tool for the working material be controlled in the work machine.
First, an explanation of a serial mechanism structure developed before a parallel mechanism structure has been emerged will be described. FIG. 1 is an exemplary view illustrating a conventional serial mechanism structure. As shown, the conventional serial mechanism structure, each link from a base 11 to a main spindle 12 has a cantilever structure at a perpendicular angle. The serial mechanism structure has some advantages that the working space is large and the software and control devices for controlling the structure are configured in a simple manner. When compared with the conventional serial mechanism structure, however, the parallel mechanism structure where the base and the main spindle are connected by means of a plurality of links has the following advantages. By these reasons, the studies for the newly proposed parallel mechanism structure have been dynamically made.
The advantages of the parallel mechanism structure are as follows: First, as the mass of inertia of a moving part decreases, the velocity and the acceleration thereof can increase; Second, as the main spindle and the base are connected by means of the plurality of links and only a tension force and a compressing force, instead of a bending force, are applied to each link, the stiffness of the machine can increase; Third, as the error of each link of the parallel mechanism structure is reflected to the main spindle on the average, the accuracy thereof can be more improved, when compared with the serial mechanism structure where the error of each link is accumulated; and Forth, when compared with most of the work machine adopting the serial mechanism structure are three-axis right angled coordinate machine, the parallel mechanism structure is basically configured to carry out six degree-of-freedom(d.o.f) motions, which can at a time work five-face and five-axis in a complete shape.
FIG. 2 is an exemplary view illustrating a hexapod structure as the conventional parallel mechanism structure. As shown, in the hexapod structure the main spindle 22 and the base 21 are connected by means of six links, and the expansion of the links enables the six d.o.f motions. The hexapod structure is called xe2x80x98Stewart platformxe2x80x99. The parallel mechanism work machine adopting the xe2x80x98Stewart platformxe2x80x99 has been manufactured by Giddings and Lewis Co. in U.S.A. The work machine achieves the six d.o.f motions, but has the disadvantages that the working space is very small and particularly, the main spindle is inclined up to about 15xc2x0 and cannot continuously sweep the lateral surfaces of the workpiece over a full 360 degree range.
Also, an xe2x80x98octahedral hexapodxe2x80x99 structure has been developed by the co-operation of the Ingersoll inc. and NIST in U.S.A. The structure is reverse to the xe2x80x98Stewart platformxe2x80x99 structure. In this case, the working space is narrow and the main spindle has the inclination angle of 30xc2x0 and additionally, the work bench is inclined at the angle of 15xc2x0. However, it is noted that the whole inclination of the xe2x80x98octahedral hexapodxe2x80x99 structure is the angle of 45xc2x0. The limitation of the hexapod structure is due to the problems that the six links connected to the main spindle interfere with each other and the rotating angle of the ball joint connecting the main spindle and the link is fixed.
A newly developed parallel mechanism structure where the inclination angle of the main spindle extends up to an angle of 90xc2x0 is disclosed in Korean Patent No. 237553 filed by the same applicant. FIGS. 3a and 3b are exemplary views illustrating the conventional parallel mechanism structure where the main spindle is inclined up to an angle of 90xc2x0, wherein FIG. 3a shows the main spindle of the inclination angle of 0xc2x0 and FIG. 3b shows the main spindle of the inclination angle of 90xc2x0.
As shown, three links 73, 74 and 75 connected to a main spindle 72 are transferred vertically along corresponding rectilinear vertical guides 83, 84 and 85, and the three vertical guides 83, 84 and 85 are transferred along a round horizontal guide 76 for the horizontal transfer at an angle of 360xc2x0. The three links 73, 74 and 75 are connected by S-R-P joints from the main spindle 72, and the vertical guides 83, 84 and 85 are connected by a Pxe2x80x2 joint with the circular horizontal guide 76. The P joint and the Pxe2x80x2 joint are driven and thus, by the six driving joints, the six d.o.f motions of the main spindle 72 can be achieved.
In this case, the xe2x80x98Sxe2x80x99 represents a spherical joint for a three-dimensional rotation. the xe2x80x98Rxe2x80x99 represents a revolution joint for an one-dimensional rotation, the xe2x80x98Pxe2x80x99 represents a prismatic joint for an one-dimensional rectilinear transfer, and the xe2x80x98Pxe2x80x2xe2x80x99 represents the prismatic joint for a circular transfer.
In the parallel mechanism structure as shown in FIGS. 3a and 3b, any (for example, the reference numeral xe2x80x9885xe2x80x99) of the vertical guides 83, 84 and 85 is arranged downward on the basis of the horizontal guide 76 and the other vertical guides 83 and 84 are arranged upward on the basis of the horizontal guide 76. The arrangement of the three horizontal guides 83, 84 and 85 in the different directions enables the limitation of the working space to be overcome, thereby ensuring a large working area.
In the parallel mechanism structure as shown in FIGS. 3a and 3b, also, the six d.o.f motions of the main spindle can be carried out with three actuators for horizontally transferring the rectilinear vertical guides 83, 84 and 85 on the vertical guide 76 and three actuators for vertically transferring the three links 73, 74 and 75 connected to the main spindle on the rectilinear vertical guides 83, 84 and 85. With
With the conventional parallel mechanism structure as shown in FIGS. 3a and 3b, the inclination angle of the main spindle is an angle of 90xc2x0, as shown in FIG. 3b and thereby, the five-face work except the bottom face is possible.
However, even in case of the inclination angle of 90xc2x0 of the main spindle, the bottom-face work for the material is not possible. Therefore, there is a need for the extension of the inclination angle of the main spindle.
Additionally, the conventional parallel mechanism structure has limitations as a motion simulator for simulating a real motion, due to the restriction of the inclination angle of the main spindle.
An object of the invention is to provide a parallel mechanism structure for controlling three-dimensional position and orientation which is capable of extending the inclination angle of a main spindle in the parallel mechanism structure as shown in FIGS. 3a and 3b, whereby in the case where it is applied in a work machine, the bottom-face work for a material is possible and in the case it is applied in a motion simulator, the inclination angle of the main spindle rotates at xc2x1360xc2x0.
To accomplish this and other objects of the present invention, there is provided a parallel mechanism structure for controlling three-dimensional position and orientation in which three links are connected to a main spindle of the mechanism and driven in two directions, namely, vertical and horizontal directions, thereby achieving six d.o.f motions, which includes: the three links comprised of a first link transferred along a circular vertical guide and second and third links transferred along corresponding rectilinear vertical guides; and a circular horizontal guide on which the circular vertical guide and the two rectilinear vertical guides are horizontally transferred.
In the parallel mechanism structure according to the present invention, the first link is connected by three-dimensional rotation joint-one-dimensional rotation joint-one-dimensional circular transfer joint (S-R-Pxe2x80x2), the second and third links are connected by three-dimensional rotation joint-one-dimensional rotation joint-one-dimensional rectilinear transfer joint (S-R-P), and the circular vertical guide and the two rectilinear vertical guides are connected by the one-dimensional circular transfer joint Pxe2x80x2 to the circular horizontal guide.